The precise mechanisms and immunoregulatory events associated with triggering of human B lymphocytes following non-specific and antigen induced stimulation have been delineated. Functionally distinct as well as overlapping immunoregulatory lymphocyte subsets have been characterized. The precise abnormalities of immunologic reactivity have been characterized in several immunologically mediated diseases such as systemic lupus erythematosus, Sjogren's syndrome, acute infectious mononucleosis, sarcoidosis and tuberculosis. For the first time, an anti-idiotypic antibody has been produced which specifically blocks the function of human B cells bearing the corresponding idiotype. Hybridoma lymphocyte cell lines have been established which are secreting antibody which binds specifically to functionally distinct subsets of human blood lymphocytes. Counter-current centrifugation techniques have been adapted which result in 95% and greater purity and yield of monocytes from human blood. These cells have been characterized functionally and structurally. Modulation of lymphocyte subsets by a number of clinically relevant pharmacologic agents have been defined. Clinical therapeutic studies have yielded extraordinarily favorable results in the cytotoxic drug approach to the systemic necrotizing vasculitides.